The present invention relates to a circuit and method for automatically compensating tracking and picture quality of a video tape recorder (VTR), in which tracking and picture quality are automatically compensated during the playback of a tape in a VTR, thereby enabling the VTR to produce optimum picture quality.
While performing reproduction in a VTR, a video head should accurately trace the video track of a tape on which video signals are recorded. That is, the position of the rotary video head must be controlled so that it corresponds to the position of the tape on which the video signal is recorded. For this reason, a 30 Hz control signal generated from the vertical sync signal of the input video signal is recorded by a control head on the control track along the bottom of the tape. Thus, the control signal is reproduced during playback, and used as a reference signal for controlling the phase of the drum and servo system.
On the other hand, the spacing between the position of the control head, i.e., the X-distance, differs slightly in all VTRs. Therefore, since the X-distance of each VTR commercially available differs from one another during playback, the tracking positions also do not match, thereby causing noise in a video cassette tape.
To decrease such noise, the tracking is automatically or manually controlled. Manual tracking adjustment is performed by a user checking the condition of the picture while turning a tracking control knob installed on the VTR. Automatic tracking adjustment is performed via software within a microcomputer.
In the conventional tracking adjusting method, the envelope levels of the video signal picked up by the head are compared while decreasing or increasing the tracking data, so that tracking is controlled in optimum state when the envelope level is maximized.
Meanwhile, drop-out of the reproduced video signal is detected and compensated in the VTR. The drop-out detection is performed every one horizontal scanning period. When the drop-out is detected, a drop-out compensation (hereinafter referred to as DOC) pulse is generated, and then, the signal delayed by one horizontal scanning period is output in current signal period, so that the drop-out is compensated, which in turn decreases noise.
At this time, although the drop-out is compensated by the DOC pulse in accordance with the drop-out detection, good picture quality cannot be obtained when a plurality of DOC pulses are generated, i.e., in case of severe drop-out.
Accordingly, since the picture quality is controlled by only comparing the envelope levels of the video signal to adjust the tracking according to the conventional automatic adjusting method, a problem remains that the deterioration of picture quality due to drop-out cannot be prevented.